The surface of Mars shows widespread aqueous activity in its early history. However, the climate for most part of Mars’ history could not sustain liquid water yet many water-carved features were formed. Groundwater can explain aqueous activity under adverse surface conditions. Many features on Mars are associated with groundwater, like ... read more valleys formed by groundwater seepage and large outflow channels, but these systems are poorly understood. I this thesis, I investigate groundwater outflow processes and resulting landscape formation in order to reconstruct the paleohydrology and paleoclimate on Mars.
Theater-headed valleys can form by groundwater seepage, but other processes can result in similar morphologies. This ambiguity hampers the interpretation of such valleys. In addition to single-valley morphology, metrics of the entire landscape shows the formative conditions. I study groundwater seepage from local and distal sources of groundwater in large sandbox experiments and provide a framework of landscape metrics indicative for groundwater seepage. Key results are that valleys fed from a distal source result in a sparsely dissected landscape of many small and a few large valleys, and a local source results in a densely dissected landscape. On Mars, Louros Valles show properties of seepage by a local source and Nirgal Vallis shows evidence for a distal source, likely groundwater originating from Tharsis.
The large outflow channels on Mars likely originate from pressurized groundwater. However, currently assumed processes cannot explain their assumed high discharges. Using large sandbox experiments and numerical modeling, I examine processes that result from pressurized groundwater. The experiments show distinct outflow processes from different pressures. Higher pressures can result in rapid outflow through fissures or in the formation of a subsurface reservoir that grows due to deformation of the surface. When this reservoir collapses, a large volume of water is expulsed to the surface. I show that the formation and collapse of such reservoir generates floods that can explain the morphologies of the largest outflow channels on Mars and their source areas.
I use the morphology from the experiments to investigate features in Ophir and Lunae Plana. Outflow sources in this region strongly relate to the tectonic structure, which likely triggered outflow from a pressurized aquifer. The pressurized groundwater outflow features are consistent with the presence of a cryosphere-confined aquifer in the Hesperian and onwards. A spatial trend of larger outflow systems at lower elevations suggests that a common aquifer was the source for many outflow channels.
The formation of a confining cryosphere in the Early Hesperian allowed for aquifer pressurization and resulted in early outflow events. The decreasing discharges of later outflow events suggest that recharge ceased during the Hesperian. The residual groundwater in the aquifer is a likely source for smaller Amazonian outflow events. Clearly, no surface hydrological cycle is necessary for groundwater outflow, nor atmospheric conditions that could sustain liquid water. Moreover, since tectonism is the most likely outflow trigger, my results show that, in contrary to currently assumed models, an episodic warm and wet climate is not a necessary condition for groundwater outflow on Mars. show less